Time division multiple access (TDMA) is a channel access method that allows multiple devices within a single network to share the same communication channel (e.g. frequency channel) by dividing the channel into different time slots. The devices transmit in sequence, one after the other, each using their own time slot. Typically, a communication channel utilising TDMA will be split into superframes with each superframe being divided into a fixed number of time slots, each time slot within each superframe being available for use by a different device. For example, for a communication channel whose individual superframes include eight time slots, that communication channel could be shared by up to eight different devices, with each device being allocated a slot within each superframe. In addition, TDMA-based communication networks usually make use of beacons, wherein a beacon is a frame periodically broadcast by a central node, base station or hub to facilitate network management functions. For example, these management functions can include clock synchronization and coordination of access and power management of the network nodes that are connected to or require connection to the central node/base station/hub. The period between transmissions of the beacon is divided into a number of slots and can be referred to as a beacon period or beacon interval, and all communication within the network during the beacon period is implemented within a superframe structure. FIG. 1 illustrates an example of a basic superframe.
Personal Area Networks (PAN), Wireless Sensor Networks (WSN), Body Area Networks (BAN) and Body Sensor Networks (BSN) are typically comprised of a number of small wireless devices or sensors that communicate with a hub or base station over relatively short distances. The small size of these devices places limits on their battery life and means that minimizing their power consumption is an important consideration. For this reason, these networks tend to use TDMA-based communication. However, given the potential number of different applications that may make use of such wireless networks and that there are likely to be a large number of networks for each application, interference between networks that are in relatively close proximity is a potential problem. In particular, the large number of such networks will likely mean that communication channels are re-used by a number of individual networks, and that mechanisms that allow these networks to coexist whilst using the same communication channel will be required.
Currently, coexistence between multiple TDMA-based beacon-enabled networks has only be achieved if each network defines a number of frames within each of its superframes as inactive, such that they can be used by neighbouring networks. This is illustrated in FIG. 2, in which a superframe is divided into a number of slots S, with A active slots such that there are (S-A) inactive slots. However, this approach has the disadvantage that it requires a lot of coordination between the networks, and the complexity of this coordination increases exponentially as the number of networks increases.
It is therefore an aim of the present invention to provide a TDMA-based communication method and system that addresses the aforementioned problems.